FIG. 1 is a sectional view illustrating a method of forming a metal insulating layer of a related semiconductor device and its problems.
Referring to FIG. 1, a metal interconnection layer pattern 120 exposes a part of the insulating layer 110 formed over a semiconductor substrate 100. A first metal insulating sub-layer 131 and a second metal insulating sub-layer 132 are sequentially laminated over the exposed surface of the insulating layer 110 and the metal interconnection layer pattern to form a metal insulating layer 130. The first metal insulating sub-layer 131 is formed of a high density plasma (HDP) oxide layer having a high gap filling performance. The second metal insulating sub-layer 132 is formed of a plasma enhanced-tetra ethyl ortho silicate (PE-TEOS) oxide layer. A first protective insulation sub-layer 141 for protecting a metal insulating layer and a chip and a second protective insulating sub-layer 142 are deposited over the metal insulating layer to form a protective insulating layer 140. The first protective insulating sub-layer 141 is an oxide layer and a second protective insulating sub-layer 142 is a nitride layer.
In the related method of forming the metal insulating layer, the first metal insulating sub-layer 131 is formed by repeating deposition and etching. Due to the step difference caused by the metal interconnection layer pattern 120, the top edges of the first metal insulating sub-layer 131 have sharp profiles as denoted by A in the drawing. Therefore, stress is caused by differing thermal expansion coefficients of the metal interconnection layer pattern 120 and the insulating layers in a subsequent thermal process. The stress can cause severe problems in the boundaries between the insulating layers because the top edges of the first metal insulating sub-layer 131 are sharp. As an example, when the thermally-induced stress reaches a threshold value, the top edges of the first metal insulating sub-layer 131 are cracked. In a severe example, the protective insulating layer 140 is also cracked so that the reliability of a device is significantly degraded.